1. Technical Field
The present disclosure relates to a device for use in orthopedic spine surgery. In particular, the present disclosure relates to a device for fixating a bone that is able to lengthen in response to bone growth.
2. Background of Related Art
The human spine is comprised of thirty-three vertebrae at birth and twenty-four as a mature adult. The vertebra includes the vertebral body and posterior elements, including the spinous process, transverse processes, facet joints, laminae, and pedicles. The vertebral body consists of a cortical shell surrounding a cancellous center. Between each pair of vertebrae is an intervertebral disc, which maintains the space between adjacent vertebrae and acts as a cushion under compressive, bending and rotational loads and motions. A healthy intervertebral disc consists mostly of water in the nucleus pulposus, which is the center portion of the disc. The water content gives the nucleus a spongy quality and allows it to absorb spinal stresses.
Scoliosis is a medical condition in which the spine is curved from side to side or front to back and may also be rotated about its long axis. Typical treatment involves observation in order to determine the rate of progression and external bracing to help ensure any future growth of the spine follows the desired path and orientation.
Surgical adjustment is warranted when the likelihood of curve or rotation progression is high or if a significant amount of pain or other general health risks are experienced. In these instances, a spinal fusion of various segments may be performed in order to stabilize the scoliotic curve. In younger patients, performing a spinal fusion is less desirable since it will interfere with the normal growth of an individual.
Growing rods have been developed to minimize the effect on the normal growth of younger patients undergoing such procedures. Growing rods provide structure, stability, and correction to the spine while allowing the rod to lengthen without the need for replacing or adding devices to the original construct.
A major disadvantage of the currently available growing rod systems is that they require a surgical procedure for manually increasing the length of the rod, usually by loosening one or more set screws, providing distraction between two rod segments, and then re-tightening. One system that works this way and is currently being marketed today is the ISOLA® by DePuy Spine, Inc. Systems such as this require a surgical procedure approximately every six months for several years. Other systems include a second device to cause the rod or construct to lengthen when an operator uses a type of telemetry to activate the device. This type of system requires an additional level of complexity using active elements and possibly some type of power source. The currently available devices do not passively allow growing rods to lengthen as the spine grows while maintaining structure and stability.